8.3.1.1 Gain Drift

The stability and temperature drift of the external gain setting resistor (R_G) also affects gain. The R_G contribution to gain accuracy and drift can be directly inferred from the gain of Equation 1.

The best gain drift of 1 ppm per degree Celsius can be achieved when the INA827 uses G = 5 without R_G connected. In this case, the gain drift is limited only by the slight temperature coefficient mismatch of the integrated 50-kΩ resistors in the differential amplifier (A₃). At gains greater than 5, the gain drift increases as a result of the individual drift of the resistors in the feedback of A₁ and A₂, relative to the drift of the external gain resistor R_G. Process improvements to the temperature coefficient of the feedback resistors now enable a maximum gain drift of the feedback resistors to be specified at 35 ppm per degree Celsius, thus significantly improving the overall temperature stability of applications using gains greater than 5.

Low resistor values required for high gains can make wiring resistance important. Sockets add to wiring resistance and contribute additional gain error (such as possible unstable gain errors) at gains of approximately 100 or greater. To ensure stability, avoid parasitic capacitances greater than a few picofarads at R_G connections. Careful matching of any parasitics on both R_G pins maintains optimal CMRR over frequency; see the Typical Characteristics section.